London equation

The London equation relates supercurrent to the electromagnetic vector potential. In a gauge with constant condensate phase it has the form $\mathbf{J}=-\mathbf{A}/({\mu }_0{\lambda }_L^2)$ and implies exponential magnetic-field screening.

The Meissner effect is the expulsion of magnetic field from the bulk of a superconductor. A static field decays from its surface over the London penetration depth.